Sharif Digital Repository

This paper proposes a new control scheme to eliminate the 3rd harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical 3rd harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a... 

DC-link voltage and output current control loops are two cascaded loops in the control structure of grid-connected inverters. A high DC-link voltage loop bandwidth (DCL-BW) provides more disturbance rejection capability for the control loop and is preferred from control system perspective. However, for stability issues, this BW is limited and must be sufficiently less than that of the current control loop. Among the different control schemes, instantaneous active reactive control (IARC) method provides the highest possible DCL-BW (i.e., 0.02 × switching frequency). Having this degree of freedom in the controller design, a proper methodology should be defined for selection of DCL-BW. In this... 

In this paper, the power quality of a single-phase photovoltaic grid connected inverter when uses active islanding detection methods is investigated. Two main groups of these methods are analyzed in this paper. The main focus is on the output power quality of PV sources for these methods. Also the variation of output current THD, while the output power changes, is explored. The variation of output current THD is measured when the parameters of active islanding detection method are changed, and the limitation of these parameters for complying power quality standards in the nominal output power is detected. ©2009 IEEE  

Serious and challengeable role in markets of low power supplies for cellular phones and other small portable devices is expected for single fuel cell in future. Single fuel cell voltage level is extremely low in comparison with its output current. According to the extremely low level of the voltage, a suitable dc/dc boost converter must be used for increasing the voltage. In this paper, a model for a single fuel cell is presented and the effect of external load variation and changing of reactant pressure on cell performance is investigated. Moreover, a predictive voltage controller for boost convertor of PEM fuel cell is presented, simulated and validated using MATLAB/Simulink. The results... 

In this paper, a novel droop method to control the power sharing of parallel uninterruptible-power-supply (UPS) systems is presented. In a clear-cut contrast to the previously reported works, the controller is a proportional-resonant controller which ensures good transient response and steady-state objectives. Furthermore, the need for sensing the output current for the power-sharing control is removed by implementing it in a software routine. This brings a less complicated and less expensive structure in which the number of feedback sensors is reduced from three to two. The droop paralleling strategy is based on the drop in the inverter output frequency and amplitude. The application of... 

Linear controllers have been widely used for controlling Active Power Filters (APFs). However, due to their limitations, a tradeoff between the bandwidth of the current control loop (CCL) and the voltage control loop (VCL) need to be made to remain stable in all conditions. This tradeoff leads to imperfect usage of the APF's capacity. Nonlinear controllers can eliminate such limitations and simultaneously remain stable in all conditions. In this paper, a new nonlinear controller for controlling the output current and the DC voltage (Vdc) of an APF is proposed. Feedback linearization method is applied on the CCL and the VCL is controlled via indirect method. In this method, an auxiliary... 

Wound-Rotor (WR) resolvers are the most widely used position sensors in applications with harsh environmental conditions. However, their performance is exposed to failure due to high risk of short circuit (SC) fault. Although the output current of the resolver is negligible, its thin copper wires increases the probability of the short circuit fault. To avoid the propagation of the turn-to turn SC fault to the whole coil and undesirable performance of the motion control drive, it is necessary to diagnose it at the very beginning of its development. Meanwhile, the first step of diagnosing faults is their modeling. Time stepping finite element analysis is the most accurate, but computationally... 

LLC resonant converter has been used widely as dc-dc converter for achieving constant dc voltage. In this paper, an LLC resonant converter, by adding an inductance to its conventional topology and considering the rectifying stage stray inductances, is proposed for an adjustable wide range regulated current source (20-200 A dc) for using as ion implanter's filament power supply. The additional inductor increases output current adjustment range and efficiency, especially at light loads. Transformer's leakage inductances and rectifying stage stray inductances have been considered. Because of these inductances, the rectifier stage always works in continuous conduction mode, and its conduction... 

In this paper, a simpler implementation of the well-known droop method for the control of parallel Uninterruptible Power Supply (UPS) systems is presented. In this method, in the power-sharing control scheme, the output current is calculated by software without the need for a current sensor, resulting in a simpler and cheaper structure. By doing so, the number of feedback sensors is reduced from three to two. The paralleling strategy uses the droop method in which the control strategy is based on the drop in the inverter output frequency and amplitude. The application of Proportional-Resonant (PR) controllers is also extended to parallel inverter and its superior performance over the...